Support Array argument

mrblib/file.rb

@@ -19,16 +19,30 @@ class File < IO
   end
 
   def self.join(*names)
-    if names.size == 0
-      ""
-    elsif names.size == 1
-      names[0]
+    return "" if names.empty?
+
+    names.map! do |name|
+      case name
+      when String
+        name
+      when Array
+        if names == name
+          raise ArgumentError, "recursive array"
+        end
+        join(*name)
       else
+        raise TypeError, "no implicit conversion of #{name.class} into String"
+      end
+    end
+
+    return names[0] if names.size == 1
+
     if names[0][-1] == File::SEPARATOR
       s = names[0][0..-2]
     else
       s = names[0].dup
     end
+
     (1..names.size-2).each { |i|
       t = names[i]
       if t[0] == File::SEPARATOR and t[-1] == File::SEPARATOR
@@ -47,7 +61,6 @@ class File < IO
     end
     s
   end
-  end
 
   def self.expand_path(path, default_dir = '.')
     def concat_path(path, base_path)

test/file.rb

@@ -77,6 +77,8 @@ assert('File.join') do
   assert_equal "/a/b/c", File.join("/a", "b", "c")
   assert_equal "a/b/c/", File.join("a", "b", "c/")
   assert_equal "a/b/c", File.join("a/", "/b/", "/c")
+  assert_equal "a/b/c", File.join(["a", "b", "c"])
+  assert_equal "a/b/c", File.join("a", ["b", ["c"]])
 end
 
 assert('File.realpath') do